Merge branch 'mysql-doc' into 'master'

Docs on running MySQL

I didn't know where to place a link from the `README.md`, but decided one would fine it either way with grep etc.

See merge request !165

doc/mysql.md

+# GitLab with MySQL
+
+Eventhough our prefered database is PostgeSQL, there are time you'd want to test your code on MySQL. This is meant as a general guideline in setting things up.
+
+## Installing MySQL
+
+On OSX, with brew installed run
+
+```
+brew install mysql
+```
+
+If you've already done this before, run 
+
+```
+brew info mysql
+```
+
+Both command will print the post install messages on how to start the server. If you're not exposing your development machine to the internet and _only_ use it for development there is no need to to secure your installation.
+
+## Setting up Rails to connect to MySQL
+
+If you ran `bundle install` before, or you've fully installed the GitLab Development Kit, the mysql gem was. To make sure the gem will be installed, remove `mysql` in `gitlab/.bundle/config` from the `BUNDLE_WITHOUT` key. Run `bundle` in the `gitlab` folder to install mysql.
+
+Configuration of the database is stored in `gitlab/config/database.yml`. Run the following command to update it:
+
+```
+sed -e 's/^  (username|password)/  # \1/' config/database.yml.mysql > config/database.yml
+```
+
+Now you can run `rake dev:setup` and test your code using MySQL for data persistance.
+
+## Reverting back to PostgreSQL for development
+
+In the GDK root:
+
+```
+rm gitlab/config/database.yml
+make
+```